People that end up in a position to care about performance are using profilers and bechmarks. This is actually the first rule: don't guess, measure.
Of course it helps when the platform has the proper tools for it. I end up using JMH and YourKit Profiler weekly, because a memory or CPU leak can crash our process and we have pretty strict reliability requirements with a single server processing about 5000 events per second - not extremely demanding, but when it crashes, we can lose money, with the redundancy infrastructure being pretty new.
Of course it helps when the platform has the proper tools for it. I end up using JMH and YourKit Profiler weekly, because a memory or CPU leak can crash our process and we have pretty strict reliability requirements with a single server processing about 5000 events per second - not extremely demanding, but when it crashes, we can lose money, with the redundancy infrastructure being pretty new.